Dinosaurs might not have been the mighty conquerors that
everyone thinks they were.

Instead of overwhelming the world with force, dinosaurs
might have instead moved in when no one was looking.

Conventional wisdom suggests that soon after dinosaurs originated
in what is now South America, they rapidly invaded every corner of the world,
defeating their rivals by virtue of strength to rule for about 160 million
years.

Now, however, a new species of dinosaur suggests that
instead of overpowering weaker species, dinosaurs came into dominance by taking
advantage of a catastrophe that wiped out the competition.

"We used to think of dinosaurs as fierce creatures that
out-competed everyone else," said researcher Timothy Rowe, a vertebrate
paleontologist at the University of Texas at Austin. "Now we're starting
to see that's not really the case."

The new dinosaur, named Sarahsaurus, was a
14-foot-long, 250-pound (4.2 meters, 113 kilograms) sauropodomorph, a
relatively small ancestor of sauropods, the largest
animals to ever walk the Earth. The dinosaur lived about 190 million years
ago in a setting much like today's Nile Valley, with lush vegetation on either
side of a river and barren desert just beyond.

Rowe and his colleagues discovered the creature in Arizona
in 1997. Excavating it proved hard, as the site was in the high desert and
prone to windstorms. Since the researchers could not reach the site by car,
they had to spend days lugging chunks of the rock-encased fossil back to camp.

"It was a rigorous challenge, the kind I love,"
Rowe told LiveScience.

Ten million years before Sarahsaurus lived, one of the
five greatest mass extinctions in Earth's history, the Triassic-Jurassic
event, wiped out many potential competitors of dinosaurs. The researchers now
reveal that Sarahsaurus and two other early sauropodomorphsmigrated to North America in separate waves
long after that extinction. At the same time, none migrated there before the
extinction.

"They were humbler, more opportunistic creatures,"
Rowe added of dinosaurs. "They didn't invade the neighborhood. They waited
for the residents to leave and when no one was watching, they moved in."

"It's the story of a recovery after a great
extinction," Rowe said. "That's what makes it poignant for me — it's
a portent of our future. We're undergoing an immense extinction right now, and
by examining the fossil record, we could get a good predictor of our
future."

Rowe was also intrigued by the new dinosaur's hands.

"Its hand is smaller than my hand, but if you line the
base of the thumbs up, this small hand is much more powerfully built than my
hand and it has these big claws," he said. "It's a very strange
animal. It's doing something with its hands that involved great strength and
power."

"They may have been digging up roots or ripping apart
rotten logs looking for small creatures," Rowe explained. "These
animals are often thought of as herbivores, but I'm not so sure of that."

Sarahsaurus also had physical traits usually
associated with gigantic animals. For example, its thigh bones were long and
straight like pillars, yet were not much larger than a human's thigh bones.

"Some of the features we thought were tied to gigantism
might instead be linked with the forceful way of life," Rowe said.
"You could imagine they fastened onto things with their front and rear
legs and arched their backs to tear things apart."

The researchers plan on scanning the fossils in greater
detail to learn more about how the dinosaurs behaved.

They detailed their findings online Oct. 6 in the journal
Proceedings of the Royal Society B.

Charles Q. Choi

Charles Q. Choi is a contributing writer for Live Science and Space.com. He covers all things human origins and astronomy as well as physics, animals and general science topics. Charles has a Master of Arts degree from the University of Missouri-Columbia, School of Journalism and a Bachelor of Arts degree from the University of South Florida. Charles has visited every continent on Earth, drinking rancid yak butter tea in Lhasa, snorkeling with sea lions in the Galapagos and even climbing an iceberg in Antarctica.